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This paper uses a fixed point theorem in cones to investigate the multiple positive
solutions of a boundary value problem for second-order impulsive singular differential
equations on the half-line. The conditions for the existence of multiple positive
solutions are established.

1. Introduction

where , , , , , with on and ; with , in which . , where and are, respectively, the left and right limits of at , , .

The theory of singular impulsive differential equations has been emerging as an important
area of investigation in recent years. For the theory and classical results, we refer
the monographs to [1, 2] and the papers [3–19] to readers. We point out that in a second-order differential equation , one usually considers impulses in the position and the velocity . However, in the motion of spacecraft one has to consider instantaneous impulses
depending on the position that result in jump discontinuities in velocity, but with
no change in position [20]. The impulses only on the velocity occur also in impulsive mechanics [21].

In recent paper [3], by using the Krasnoselskii's fixed point theorem, Kaufmann has discussed the existence
of solutions for some second-order boundary value problem with impulsive effects on
an unbounded domain. In [22] Sun et al. and [23] Liu et al., respectively, discussed the existence and multiple positive solutions
for singular Sturm-Liouville boundary value problems for second-order differential
equation on the half-line. But the Multiple positive solutions of this case with both
singularity and impulses are not to be studied. The aim of this paper is to fill up
this gap.

The rest of the paper is organized as follows. In Section 2, we give several important
lemmas. The main theorems are formulated and proved in Section 3. And in Section 4,
we give an example to demonstrate the application of our results.

2. Several Lemmas

has a unique solution for any . Moreover, this unique solution can be expressed in the form

(22)

where is defined by

(23)

Remark 2.2.

It is easy to prove that has the following properties:

(1) is continuous on

(2) is continuous differentiable on , except ,

(3),

(4),

(5),

(6)for all , , , where

(24)

Obviously, .

For the interval , and the corresponding in Remark 2.2, we define = : , and exist, . = exists. , and . It is easy to see that is a Banach space with the norm , and is a positive cone in . For details of the cone theory, see [1]. is called a positive solution of BVP (1.1) if for all and satisfies (1.1).

As we know that the Ascoli-Arzela Theorem does not hold in infinite interval , we need the following compactness criterion:

The function is a solution of the BVP (1.1) if and only if satisfies the equation

(25)

The proof of this result is based on the properties of the Green function, so we omit
it as elementary.

Define

(26)

Obviously, the BVP (1.1) has a solution if and only if is a fixed point of the operator defined by (2.6).

Let us list some conditions as follows.

There exist two nonnegative functions: , such that . , may be singular at . , , are continuous.

,

Lemma 2.7.

If are satisfied, then for any bounded open set , is a completely continuous operator.

Proof.

For any bounded open set , there exists a constant such that for any .

First, we show that is well defined. Let . From , we have , where , , and

(27)

Hence, is well defined. For any , we have

(28)

Thus, by the Lebesgue dominated convergence theorem and the fact that is continuous on , we have, for any , ,

(29)

Therefore, . By the property (3) of , it is easy to get .

On the other hand, by (2.6) we have, for any and ,

(210)

Then by , the property (5) of Remark 2.2 and the Lebesgue dominated convergence theorem, we
have

(211)

Thus .

For any , we get

(212)

So

(213)

On the other hand, for we obtain

(214)

Thus .

Next, we prove that is continuous. Let in , then We prove that . For any , by , there exists a constant such that

(215)

On the other hand, by the continuities of on and the continuities of on , for the above , there exists a such that, for any , ,

(216)

From , for the above , there exists a sufficiently large number such that, when , we have

(217)

Therefore, by (2.15)–(2.17), we have, for ,

(218)

This implies that the operator is continuous.

Finally we show that is a compact operator. In fact for any bounded set , there exists a constant such that for any . Hence, we obtain

(219)

Therefore, is uniformly bounded in .

Given , for any , as the proof of (2.9), we can get that are equicontinuous on . Since is arbitrary, are locally equicontinuous on . By (2.6), , , and the Lebesgue dominated convergence theorem, we have

(220)

Hence, the functions from are equiconvergent. By Lemma 2.3, we have that is relatively compact in . Therefore, is completely continuous. This completed the proof of Lemma 2.7.

3. Main Results

For convenience and simplicity in the following discussion, we use the following notations:

(31)

Theorem 3.1.

Let hold. Then the BVP (1.1) has at least two positive solutions satisfying if the following conditions hold:

there exists a such that for all , a.e. .

Proof.

By the definition of and , for any , there exist such that

(32)

Define the open sets

(33)

Let , then . Now we prove that

(34)

If not, then there exist and such that . Let then for any we have

(35)

This implies , a contradiction. Therefore, (3.4) holds.

That by the definition of and , for any there exist such that

(36)

Define the open sets:

(37)

As the proof of (3.4), we can get that

(38)

On the other hand, for any , choose in such that

(39)

By the definition of , , for the above , there exists , when ; thus, we have

(310)

Define

(311)

Then, for any and , we can obtain

(312)

Therefore,

Thus, we can obtain the existence of two positive solutions and satisfying by using Lemma 2.4 and Remark 2.5, respectively.

Using a similar proof of Theorem 3.1, we can get the following conclusions.

Theorem 3.2.

Let hold. Then the BVP (1.1) has at least two positive solutions satisfying if the following conditions hold:

there exists such that , for all , a.e. .

Corollary 3.3.

In Theorems 3.1 and 3.2, if conditions and are replaced by and , respectively, then the conclusions also hold.

or or

, , , .

Remark 3.4.

Notice that, in the above conclusions, we suppose that the singularity only exist
in , that is, as . If we permit as or and as , then the discussion will be much more complex. Now we state the corresponding results.

Let us define the following.

There exist four nonnegative functions , such that , and is nondecreasing on . , , are continuous.

, , where ,

Theorem 3.5.

Suppose hold, then the BVP (1.1) has at least two positive solutions satisfying if hold.

Proof.

Define , for all . We only need to proove is a completely continuous operator. Then the rest of the proof is the same as that
Theorem 3.1. Notice that

(313)

and change to , , , then the same as the proof of Lemma 2.7, it is easy to compute that is a completely continuous operator.

Corresponding to Theorem 3.2 and Corollary 3.3, there are Theorem 3.6 and Corollary
3.7. We just list here without proof.

Theorem 3.6.

Suppose hold, then the BVP (1.1) has at least two positive solutions satisfying , if hold.

Corollary 3.7.

In Theorems 3.5 and 3.6, if conditions and are replaced by and , respectively, then the conclusions also hold.

4. Example

To illustrate how our main results can be used in practice we present the following
example.

Example 4.1.

Consider the following boundary value problem:

(41)

Conclusion 1.

BVP (4.1) has at least two positive solutions , satisfying .

Proof.

Let , , , . Then by simple computation we have

(42)

where . Furthermore, and

(43)

Let . Then . Thus are satisfied. It is easy to get that . Let . Then

(44)

Hence, are satisfied. Therefore, by Corollary 3.3, problem (4.1) has at least two positive
solutions , satisfying . The proof is completed.

Acknowledgment

This work is supported by the National Nature Science Foundation of P. R.China (10871063)
and Scientific Research Fund of Hunan Provincial Education Department (07A038), partially
supported by Ministerio de Educacion y Ciencia and FEDER, Project MTM2007-61724, and
by Xunta de Galicia and FEDER, project no.PGIDIT06PXIB207023PR.